The present invention relates to an image printing apparatus such as a laser beam printer and, more particularly to an image printing apparatus wherein an image description area is controlled in the image printing apparatus. The present invention relates to a laser beam printer as a page printer and, more particularly to a laser beam printer wherein an image description area is controlled in the laser beam printer.
A conventional image printing apparatus will be explained by referring to a laser beam printer. A conventional laser beam printer construction includes generally a video signal reception means which receives a video signal from a host means. Such a video signal defines an "on-off" control of a laser diode for every picture element individually.
A laser beam is scanned in accordance with this received video signal on a surface of a photosensitive material member such as a printing paper through various means such as a laser drive means, F.crclbar. lens and a polygon mirror rotated by a polygon motor.
A two-dimensional image is formed on the surface of the photosensitive material member by rotating the photosensitive material member, for example the surface of the printing paper as the recording medium. Such an electrostatic latent image is output using a xerography process.
In the above stated conventional laser beam printer construction, an optical sensor is arranged on a laser beam scanning line (a, main scanning direction) and detects a write-out start point of a description area in the laser beam printer.
Under the standard of this laser beam detection signal of the optical sensor generated from the video signal reception means, a horizontal synchronizing signal which synchronizes with the laser beam detection signal from the optical sensor is transmitted to the host means.
In this conventional laser beam printer construction, under the standard of such a transmitted horizontal synchronizing signal, the host means transmits a video signal having N scanning parts to the video signal reception means.
Further, in a printing paper transportation direction (an auxiliary scanning direction), similarly to the above horizontal synchronizing signal, a vertical synchronizing signal which synchronizes with the laser beam detection signal is transmitted to the host means.
Under the standard of this vertical synchronizing signal, the host means transmits a picture element having M scanning parts to the video signal reception means as a video signal. The printing having one page part is finished in accordance with a modulation of the laser diode within the description area which is constructed by the picture elements having a sum of N.times.M parts.
Therefore, according to the conventional laser beam printer construction, there are various problems with the host means receiving picture element data having N.times.M parts of what kind of patterns; further in the description area of the laser beam printer, the laser beam is constructed to control even a blank portion existing in the printing paper in accordance to white data from the host means by the laser beam drive means.
According to the above stated conventional laser beam printer, when the host means is a word processor, for example, and an operator can variable and frequently set a format including a blank portion in the word processor, it is necessary to transmit all of the picture elements having N.times.M parts into the laser beam printer as the video signal.
Further, the blank portions in the photosensitive material member (the printing paper) in the laser beam printer, which exists respectively at the left portion and the right portion and the upper portion and the lower portion, are treated as a part of the description data and are tested without a protection means, accordingly the high quality of the laser beam printer cannot be assured due to the malfunction in the laser diode and laser drive means, for example. and the malfunction causes improper description data.